Starting-rheostat.



No. 747,821. V PATENTED DEC. 22 1903.

H. B. WILSON. STARTING RHEOSTAT.

APPLICATION FILED AUG. 21, 1902. I0 MODEL.

Fig I.

WiCnesse: InvenLZor:

Howard BWi son.

1 M M QQM UNITED STATES latented December 22, 1903.

PATENT OFFICE.

HOWARD B. WILSON, OF SOHENEOTADY, NEWV YORK, ASSIGNOR TO GEN- ERALELECTRIC COMPANY, A CORPORATION OF NEW YORK.

STARTING-RHEOSTAT.

E-IPEGIFIGATION forming part of Letters Patent N 0. 747,821, datedDecember 22, 1903.

Application filed August 21, 1902.

T aZZ tub/017i, it may concern:

Be it known that I, HOWARD B. WILSON, a citizen of the United States,residing atSchenectady, county of Schenectady, State of New York, haveinvented certain new and useful Improvements in Starting-Rheostats,ofwhich the following is a specification.

This invention relates to electrical apparatus in which current passesfrom a contact IO device to a plurality of separate contact-segments insuccession; and the object of the invention is to divide the currentintotwo substantially equal fractional parts, so that the sparking at thecontacts maybe cut down.

I attain this result by equipping the contact device with two brushesarranged in tandem, or one behind the other, connected in parallel, andeach bearing on its own separate segment, so that the current will passthrough them simultaneously into two adjacent contact-segments as thedevice is moved relatively to the plurality of segments. The totalcurrent through any two adjacent contact-segments is thus'divided intofractional portions, preferably equal, and the result is a greatdiminution of sparking. Where there is a drop in potential between thesegments,

I make the resistance of the branch including the leading brushsuflicient to produce an equal drop, so that the current in the twobranches will be as nearly equal as possible.

The invention is capable of avariety of applicationssuch, for instance,as commutator-brushes for dynamo-electric machines; but for the sake ofsimplicity I shall show and describe it in. connection with astartingrheostat for electric motors. In such a device I ascertain theaverage resistance between the steps and provide the switch-arm with twotandem brushes, the leading one of a material, such carbon or graphite,ottering a resistance equal to the average between the steps, and theother of a material of low resistance, such as copper. This causes the45 current to divide equally between the two brushes in flowing to thesegment under the carbon brush, one half going by way of the carbonbrush and the other half by way of the copper brush and theresistance-coil per- Serial No. 120,431. (No model.)

manently connected between the two seg- 5o inents.

In the accompanying drawings, Figure 1 is a front elevation of astarting-rheostat embodying my invention. Fig. 2 is an edge view of thesame, and Fig. 3 is a cross-section of the switch-arm through thebrushes.

The insulatingbase 1, line-terminals 2, shunt field-coil terminal 3,rheostat contactsegments 4, insulating dead-segment 5, novoltagerelease-electromagnet 6, and movable 6o switch member 7 are all as usualin devices of this kind and need no detailed description. The customarycircuits are indicated by the dotted lines in Fig. 1. The movable memberor switch-arm carries a tailpiece 8, on which is a contact-block 9,preferably of carbon, which closes the circuit 10 from the switch-arm tothe stationary block 11 and thence to the first rheostat-segment -l whenthe switch-arm is in the 01? position and the brushes rest on thedead-segment 5.

The brushes l2 and 13 carried by the switcharin are composed,respectively, of high and low resistance material, such as carbon andcopper. They are insulated from the arm and from each other, and each isconnected with the arm by a short lead 14. A divided flat spring 15presses them against the contactsegments 4. The carbon brush 12 is infront of the copper brush 13, so that the carbon is the first to makecontact with the next segment as the arm is moved to cut out theresistance-coils of the rheostat.

The brushes bear on two adjacent segments, so that the current flowingthroughthe switcharm must divide between the two to reach the segmentunder the carbon brush. By making the resistance of the carbon brushequal to the average resistance of the rheostat-coils between thesegments the fractional 0 parts of the current will be substantiallyequal. The result is the same asif the rheostat were divided into twiceas many steps, and the tendency to spark is reduced accordingly.

What I claim as new, and desire to secure by Letters Patent of theUnited States, is-

1. In electrical apparatus, the combination witha plurality ofcontact-segments, of arelatively movable contact device comprising twobrushes whose resistance difiers as the resistance between the segments,the leading brush having the higher resistance.

2. In electrical apparatus, the combination witha plurality ofcontact-segments, of a relatively movable contact device comprising twobrushes arranged one behind the other and connected in parallel, theleading brush having as much higher resistance than the one behind it asthe drop in potential between the segments.

3. In a stai'tingrheostat, a movable switch member provided with twotandem brushes insulated from each other andconnected in parallel, theleading brush being of considerably higher resistance than the others.

4. In a starting-rheostat, a movable switch member provided with twotandem brushes insulated from each other and connected in parallel, theleading brush being of carbon and the other brush of metal.

5. In a starting-rheostat, the combination with a plurality of segmentsconnected through resistance-coils, of a movable switch member providedwith two tandem brushes connected in parallel and adapted to bear on twoadjacent segments respectively, the resistance of the leading brushbeing substantially equal to that of the coil between the segments.

In witness whereof I have hereunto set my hand this 19th day of August,1902.

HOWARD B. WILSON.

Witnesses:

BENJAMIN B. HULL, JOSEPH A. L. ENDRES.

